U.S. patent number 6,086,980 [Application Number 08/993,243] was granted by the patent office on 2000-07-11 for metal working drill/endmill blank and its method of manufacture.
This patent grant is currently assigned to Sandvik AB. Invention is credited to Stephen Foster, Alistair Grearson, Gary McCarthy, Helene Ouchterlony.
United States Patent |
6,086,980 |
Foster , et al. |
July 11, 2000 |
Metal working drill/endmill blank and its method of manufacture
Abstract
A cemented carbide drill/endmill blank and method of manufacture
thereof wherein the drill/endmill includes a core and a surrounding
tube with improved technological properties. The difference in
Co-content between the core and tube is 1-10 wt-% units and the
cubic carbide content is 8-20 wt-% in the tube and 0.5-2 wt-% in
the core.
Inventors: |
Foster; Stephen (West Midlands,
GB), McCarthy; Gary (West Midlands, GB),
Grearson; Alistair (West Midlands, GB), Ouchterlony;
Helene (Ingaro, SE) |
Assignee: |
Sandvik AB (Sandviken,
SE)
|
Family
ID: |
26662829 |
Appl.
No.: |
08/993,243 |
Filed: |
December 18, 1997 |
Current U.S.
Class: |
428/212; 407/119;
427/419.1; 427/419.2; 427/419.7; 428/325; 428/334; 428/698;
428/701; 428/702; 51/307; 51/309; 75/228; 75/236; 75/237; 75/241;
75/242 |
Current CPC
Class: |
B22F
7/06 (20130101); C22C 29/08 (20130101); B22F
2005/001 (20130101); Y10T 407/27 (20150115); Y10T
428/252 (20150115); Y10T 428/263 (20150115); Y10T
428/24942 (20150115) |
Current International
Class: |
B22F
7/06 (20060101); C22C 29/08 (20060101); C22C
29/06 (20060101); B32B 007/00 () |
Field of
Search: |
;428/698,325,216,334,336,701,702,712 ;51/295,307,309 ;407/119
;75/228,236,237,241,242 ;427/419.1,419.2,419.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
977873 |
|
Jun 1951 |
|
FR |
|
6137 |
|
Jul 1952 |
|
DE |
|
Primary Examiner: Turner; Archene
Attorney, Agent or Firm: Burns, Doane, Swecker & Mathis,
L.L.P.
Claims
What is claimed is:
1. A cemented carbide drill/endmill blank comprising a core of one
cemented carbide grade and a surrounding tube of another cemented
carbide grade, the blank having a difference in Co-content between
the core and tube of 1-10 wt-% units, the tube having a cubic
carbide content of 8-20 wt-% and the core having a cubic carbide
content of 0.5-2 wt-%.
2. The cemented carbide drill/endmill blank of claim 1, wherein the
core includes 5-20% Co, 0.5-2 wt-% cubic carbides, balance WC.
3. The cemented carbide drill/endmill blank of claim 1, wherein the
tube includes 5-25 wt-% Co, 8-20 wt-% carbides and/or carbonitrides
of Ti, Ta and/or Nb, balance WC.
4. The cemented carbide drill/endmill blank of claim 1, wherein the
core and tube are joined by a 300-500 .mu.m wide transition zone
wherein the Co content varies such that a difference in Co-content
between the core and tube is at least 2 wt-% units.
5. The cemented carbide drill/endmill blank of claim 1, wherein
prior to sintering the difference in Co-content between the core
and tube is greater than 3 wt-% units, the cemented carbide grade
of the core has a grain size of <10 .mu.m and the cemented
carbide grade of the tube has a grain size of <10 .mu.m, and
wherein after sintering the difference in Co-content between the
core and tube is less than 5 wt-% units.
6. The cemented carbide drill/endmill blank of claim 1, wherein the
cemented carbide grade of the core has a grain size of 0.5-5 .mu.m
and the cemented carbide grade of the tube has a grain size of
0.5-3 .mu.m.
7. The cemented carbide drill/endmill blank of claim 1, wherein the
tube has a diameter of 5-35 mm.
8. The cemented carbide drill/endmill blank of claim 1, wherein the
tube includes one or more flutes ground into an outer surface
thereof.
9. The cemented carbide drill/endmill blank of claim 1, wherein the
tube is coated with one or more carbide, nitride, carbonitride or
oxide coatings.
10. A method of drilling stainless steel with the cemented carbide
drill/endmill blank of claim 1.
11. A method of making the cemented carbide drill/endmill blank of
claim 1 comprising steps of compacting the cemented carbide powder
of the core followed by compacting the cemented carbide powder of
the tube around the core.
12. The method of claim 11, further comprising sintering the
compacted core and compacted tube such that the core and tube are
joined by a 300-500 .mu.m wide transition zone wherein the Co
content varies such that a difference in Co-content between the
core and tube is at least 2 wt-% units.
13. The method of claim 11, further comprising forming at least one
groove in an outer periphery of the core prior to compacting the
tube around the core.
14. The method of claim 11, further comprising forming coolant
holes in the blank.
15. The method of claim 11, further comprising sintering the
compacted core and compacted tube such that the Co content of the
core decreases and the Co content of the tube increases.
16. The method of claim 11, further comprising grinding at least
one flute into the blank.
17. The method of claim 11, wherein the core includes 5-20% Co,
0.5-2 wt-% cubic carbides, balance WC, and the tube includes 5-25
wt-% Co, 8-20 wt-% carbides and/or carbonitrides of Ti, Ta and/or
Nb, balance WC.
18. The method of claim 11, wherein the cemented carbide grade of
the core has a grain size of <10 .mu.m, the cemented carbide
grade of the tube has a grain size of <10 .mu.m, and the core
has a diameter of 40-60% of the tube diameter.
19. The method of claim 11, wherein the tube has a diameter of 5-35
mm.
20. The method of claim 11, further comprising coating the tube
with one or more carbide, nitride, carbonitride or oxide coatings.
Description
FIELD OF THE INVENTION
The present invention relates to a cemented carbide body,
preferably a cylindrical body consisting of at least two grades
with individually different compositions, microstructures and
properties, especially a body aimed at acting as a blank for a
drilling, endmilling or deburring tool.
BACKGROUND
In drilling tools the demands on the periphery and on the center
are different with respect to wear resistance and toughness. In
drill bits for rock drilling the demands differ between the surface
(wear resistance) and the inner part (toughness) as discussed in
U.S. Pat. No. 5,541,006, in which is emphasized the use of two
grades in a rock drilling bit. The grades are both straight grades
with tungsten carbide and Co. Much attention is given to the
ability to control the Co migration for which, in this case, an
abrupt or discrete change of composition at the interface between
the regions is preferred. This problem is also solved by Fischer
with the technique known as Dual-Phase or DP-technique, U.S. Pat.
No. 4,743,515. Tools as wear parts, rolling rings and
slitter/trimming knifes can be manufactured with a method described
in U.S. Pat. No. 5,543,235.
These patents, though, deal with combinations of grades containing
only WC--Co or WC--Ni. They also refer to applications where just
one of the grades is in contact with the work piece material, and
the other serves as an `equalizer` or carrier` of pressure or
impact.
One patent dealing with cemented carbide drills containing cubic
carbides is U.S. Pat. No. 4,971,485, but in that case the WC--Co
grade is used in the shaft to avoid damage due to vibrations
emanating from the machine.
The present invention relates to a compound cemented carbide body
consisting of a core of a tough grade and a surrounding tube of a
more wear resistant grade that are both in active contact with the
work piece material. The problem when making such a compound body
is to avoid the formation of cracks in the outer part or voids and
significant porosity at the interface between the two parts due to
differences in shrinkage during sintering. In addition, too high
stresses in the interface make further manufacturing, e.g.,
slitting and grinding, impossible. Another problem can be the
migration of the binder phase during sintering which results in a
leveling of the binder phase content in the two parts. The
combination of grades has to fulfil the demands on toughness and
wear resistance in the center as well as in the periphery. The
grades also have to be compatible with respect to pressing
conditions and sintering conditions.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome shortcomings of the
prior art.
According to the invention it has been found possible that by a
proper choice of composition and microstructure of the two grades
the above mentioned problems can be avoided. More particularly, the
invention relates to a drill blank with a core of a WC--Co-grade
surrounded by a tube of a grade containing also carbides and/or
carbonitrides of the elements in group 4-6, preferably Ti, Ta and
Nb.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows in 6.times. magnification a cross section of a drill
blank according to the invention wherein A shows the core and B
shows the tube; and
FIG. 2 shows in 200.times. magnification the diffuse interface
between the two grades.
DETAILED DESCRIPTION OF THE INVENTION
Drill blanks according to the invention consist of a core and a
surrounding tube. The core contains after sintering a Co content of
<30, preferably 5-20, most preferably 10-15 wt-% Co, balance WC.
In addition to WC, the tube grade has >5 wt-% Co and 5-25,
preferably 8-20 wt-%, most preferably 10-15 wt-% of one or more of
the carbides and/or carbonitrides of the elements in Groups 4-6 of
the Periodic Table, preferably Ti, Ta and Nb. The difference in Co
content between core and tube is 1-10 wt-% units, preferably 2-4
wt-% units. There is a 300-500 .mu.m wide transition zone measured
as a change in Co-content by microprobe analysis. The core may
optionally contain 0.5-2 wt-% cubic carbides.
The grain size of the core grade is <10 .mu.m, preferably 0.5-5
.mu.m, most preferably 0.5-3 .mu.m. The tube grade has a grain size
of <10 .mu.m, preferably 0.5-3 .mu.m, most preferably 0.5-1.5
.mu.m.
Blanks according to the invention are made by powder metallurgical
methods including compacting in two steps. As an example, a rod
with length around 300 mm and diameter 5-15 mm consisting of 10-30
wt-% Co and balance WC with grain size <10 .mu.m is pressed.
Preferably, this rod has a grooved form which provides a keying
action between it and the surrounding tube. Then a tube of a
desired diameter is pressed around the outside of the rod to final
green density. The size of the core is preferably 40-60% of the
total diameter of the blank. If desired the drill blank can be
provided with coolant holes by methods known to those skilled in
the art. It has been found that if the difference in Co-content
between the tube grade and the core grade is 0-15 wt-% units,
preferably 5-10 wt-% units and the tube contains cubic carbides as
mentioned above, the blank can be sintered without formation of
cracks or voids between the core and the tube.
The pressing and sintering properties of the original grade powders
are of utmost importance to get a good result. Pressing conditions
are determined by thermal expansion coefficient, shrinkage and
required pressing pressure for the grades used. It is within the
purview of the skilled artisan to determine these conditions by
experiments. Sintering is preferably performed at 1350-1450.degree.
C.
After sintering, the rods are usually cut into drill blanks of
50-150 mm, preferably 80-120 mm length. The most useful diameter
range is 5-35 mm, preferably 5-20 mm.
The flute is ground with for example a diamond wheel at 18-20 m/sec
with a feed of 60-80 mm/min.
In an alternative embodiment, a drill top of length/diameter ratio
of 0.5-5.0 is used which is brazed to a shaft.
After finish grinding, drills of the above mentioned kind are
suitable for coating by vapor deposition such as PVD with carbide,
nitride, carbonitride or oxide or combinations thereof, e.g., TiN,
TiAlN, Ti(C,N).
Drills of this invention are particularly useful for machining of
stainless steel and normal steel.
EXAMPLE 1
Drills according to the invention were produced by pressing in two
stages. First, a cylindrical rod having a length of 300 mm and
diameter of 11 mm with a composition of 20 wt-% Co and 80 wt-% WC
and grain size 2 .mu.m was pressed. Then, a powder with original
composition of 11 wt-% Co, 6.1 wt-% TaC, 1.9 wt-% NbC, 4 wt-% TiC
and balance WC and grain size 2.5 .mu.m was pressed around the
outside of the rod to final green density. Some of the drills were
provided with coolant holes according to a technique well known in
the art. After sintering, the Co content of the core grade had
decreased from 20 to 14 wt-% and the Co content in the tube grade
had increased to 12 wt-%. In addition, significant amounts of the
cubic carbides could be detected in the center of the core.
After sintering, the rods were cut into drill blanks of 105 mm
length and 14 mm in diameter. The flute and top and bottom of the
blanks were ground to final appearance.
EXAMPLE 2
PVD TiN coated drills from Example 1 were tested by drilling in
stainless steel AISI 316. Single grade drills of the two original
grades used in the drills from Example 1 and one fine grained 1
.mu.m WC-- 10 wt-% Co grade normally used in these cutting
conditions were used as references.
The following three test conditions were used with external
cooling:
a) v=50 m/min, f=0.14 mm/rev
b) v=82 m/min, f=0.12 mm/rev
c) v=32 m/min, f=0.22 mm/rev
In test a) the drill according to the invention lasted 357 holes,
while the single grade drills were worn out after 207 holes (single
grade fine grained WC--Co), 149 holes (single grade 11 wt-% Co, 12
wt-% Ta, Nb, Ti carbides, rest WC) and 55 holes (single grade 20
wt-% Co).
At higher speed and lower feed in test b) the drill according to
the invention and the fine grained grade made 192 holes while the
other single grades made 126 holes (single grade 9 wt-% Co) and 22
holes (single grade 20 wt-% Co).
At lower speed with higher feed in test c) the result was 179 holes
for the drill according to the invention while the fine grained
grade made 128 holes and the 20 wt-% Co grade made 41 holes before
they were stopped because of cracks or wear.
EXAMPLE 3
Drills from Example 1 provided with internal coolant supply holes
were tested by drilling in stainless steel. In this test an
ordinary P40 drill was used as a reference.
At increased speed (100 m/min, f=0.16 mm/rev) the drill according
to the invention drilled 550 holes while the P40 reference drill
was totally broken down after only 3 holes.
At normal speed but a higher feed (50 m/min, f=0.25 mm/rev) the P40
drill suffered from chipping after 660 holes and the drill
according to the invention was still working after 1100 holes.
At ordinary cutting speed and feed (50 m/min, f=0.16 mm/rev) the
two drills were equal in performance and the test was interrupted
after 1100 holes.
EXAMPLE 4
Drills from Example 1 provided with internal coolant supply holes
were tested on austenitic stainless steel, AISI 304. In this test
ordinary P40 and sub-micron K20 drills were used as references.
At normal speed (50 m/min, f=0.16 mm/rev) the drill according to
the invention was still working after 2668 holes while the P40 and
sub-micron K20 drills were worn out after 2011 and 242 holes,
respectively.
At increased feed but normal speed (50 m/min, f=0.30 mm/rev) the
drill according to the invention completed 520 holes while the P40
and sub-micron K20 drills completed 110 and 22 holes,
respectively.
At increased speed (100 m/min, f=0. 16 mm/rev) the drill according
to the invention achieved 198 holes, while the P40 and K20 drills
broke down after 1 or 2 holes.
EXAMPLE 5
Drills from Example 1 with internal coolant supply holes, but in 10
mm diameter and coated with Ti(C,N) and TiN were tested by drilling
AISI 316 (SS2353), 30 mm through hole drilling. In this test an
ordinary fine grained PVD coated drill was used as a reference.
Several cutting data combinations were used, and from the results
shown below, the drill according to the invention has a much
broader working range compared to a conventional drill.
The table below shows the number of holes achieved with the drills
used in the test. The test was stopped after 1300 holes even though
the drills were not worn out.
______________________________________ Cutting Data Speed (m/min)
40 40 40 60 60 60 Feed (mm/rev) 0.13 0.20 0.25 0.13 0.20 0.22
______________________________________ Ordinary drill 600 100 --
100 3 -- Drill according to the >1300 400 500 >1300 >1300
500 invention ______________________________________
The foregoing has described the principles, preferred embodiments
and modes of operation of the present invention. However, the
invention should not be construed as being limited to the
particular embodiments discussed. Thus, the above-described
embodiments should be regarded as illustrative rather than
restrictive, and it should be appreciated that variations may be
made in those embodiments by workers skilled in the art without
departing from the scope of the present invention as defined by the
following claims.
* * * * *